转自：http://www.cnblogs.com/_zjl/archive/2011/04/08/2009087.html

XmlDatasetConvert.cs
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.IO;
using System.Xml;

namespace XmlDesign
{
    class XmlDatasetConvert
    {
        //将xml对象内容字符串转换为DataSet
        public static DataSet ConvertXMLToDataSet(string xmlData)
        {
            StringReader stream = null;
            XmlTextReader reader = null;
            try
            {
                DataSet xmlDS = new DataSet();
                stream = new StringReader(xmlData);
                //从stream装载到XmlTextReader
                reader = new XmlTextReader(stream);
                xmlDS.ReadXml(reader);
                return xmlDS;
            }
            catch (System.Exception ex)
            {
                throw ex;
            }
            finally
            {
                if (reader != null) reader.Close();
            }
        }

//将xml文件转换为DataSet
        public static DataSet ConvertXMLFileToDataSet(string xmlFile)
        {
            StringReader stream = null;
            XmlTextReader reader = null;
            try
            {
                XmlDocument xmld = new XmlDocument();
                xmld.Load(xmlFile);

DataSet xmlDS = new DataSet();
                stream = new StringReader(xmld.InnerXml);
                //从stream装载到XmlTextReader
                reader = new XmlTextReader(stream);
                xmlDS.ReadXml(reader);
                //xmlDS.ReadXml(xmlFile);
                return xmlDS;
            }
            catch (System.Exception ex)
            {
                throw ex;
            }
            finally
            {
                if (reader != null) reader.Close();
            }
        }

//将DataSet转换为xml对象字符串
        public static string ConvertDataSetToXML(DataSet xmlDS)
        {
            MemoryStream stream = null;
            XmlTextWriter writer = null;

try
            {
                stream = new MemoryStream();
                //从stream装载到XmlTextReader
                writer = new XmlTextWriter(stream, Encoding.Unicode);

//用WriteXml方法写入文件.
                xmlDS.WriteXml(writer);
                int count = (int)stream.Length;
                byte[] arr = new byte[count];
                stream.Seek(0, SeekOrigin.Begin);
                stream.Read(arr, 0, count);

UnicodeEncoding utf = new UnicodeEncoding();
                return utf.GetString(arr).Trim();
            }
            catch (System.Exception ex)
            {
                throw ex;
            }
            finally
            {
                if (writer != null) writer.Close();
            }
        }

//将DataSet转换为xml文件
        public static void ConvertDataSetToXMLFile(DataSet xmlDS,string xmlFile)
        {
            MemoryStream stream = null;
            XmlTextWriter writer = null;

try
            {
                stream = new MemoryStream();
                //从stream装载到XmlTextReader
                writer = new XmlTextWriter(stream, Encoding.Unicode);

//用WriteXml方法写入文件.
                xmlDS.WriteXml(writer);
                int count = (int)stream.Length;
                byte[] arr = new byte[count];
                stream.Seek(0, SeekOrigin.Begin);
                stream.Read(arr, 0, count);

//返回Unicode编码的文本
                UnicodeEncoding utf = new UnicodeEncoding();
                StreamWriter sw = new StreamWriter(xmlFile);
                sw.WriteLine("<?xml version=\"1.0\" encoding=\"utf-8\"?>");
                sw.WriteLine(utf.GetString(arr).Trim());
                sw.Close();
            }
            catch( System.Exception ex )
            {
                throw ex;
            }
            finally
            {
                if (writer != null) writer.Close();
            }
        }

}
}